/targetraid
/cast (Insert Decurse Spell Here)
Is it nearly as good? No. Not even close. But combined with a mod that lists people with curses nearby (NOT a broken functionality) it works well enough for mass-decursing (a la Chromaggus or Noth). It's the same functionality as Tab, by the way, but for raid members - and with many of the same restrictions (have to be facing them, etc.)
Keep in mind that you can't use, say, Abolish Poison/Disease with this macro (since it'll always cast regardless of if there's a posion or disease on your actual target) but demagic and decurse will work perfectly fine... and you can still Cure Disease/Poison.